1. Field of the Invention
The present invention relates to a converter for satellite broadcast reception, and particularly to a structure for fixing a circuit board to a chassis.
2. Description of the Prior Art
FIG. 7 is a general view of an antenna incorporating a converter for satellite broadcast reception. Reference numeral 1 represents the converter proper, which is composed of an RF (radio frequency) circuit board built in a chassis 1a made of aluminum or zinc, and which is covered with a cabinet 2. A radio wave transmitted from a satellite is reflected from a parabolic antenna 3 so as to be received by a horn portion 4 provided at one end of the converter proper 1, and is then fed to the circuit board built in the converter. Thereafter, the received radio wave, which is in the 12 GHz band, is converted into a signal in the 1 GHz band by the circuit board built in the converter, and is then fed to a tuner unit by way of a coaxial cable 5.
Quite naturally, these components are expected to endure a harsh outdoor environment all over the world, i.e. all kinds of hostile use conditions including natural phenomena such as heating by sunlight, an abrupt temperature fall by a squall or the like, vibrations by a wind storm, and day-to-night temperature variations. Thus, the circuit board needs to be fixed to the chassis in such a way as to maintain stable grounding even in such an environment, and, in particular in a converter for satellite broadcast reception, which is designed for use in an extremely high frequency band, it is essential to secure good grounding.
Moreover, in particular in an apparatus such as a converter for satellite broadcast transmission/reception designed for use in an outdoor environment, it is necessary to enable it to endure abrupt temperature variations (e.g. in a range from xe2x88x9240xc2x0 to 70xc2x0), vibrations (e.g. the vibrations of an antenna), and the like by devising a structure that absorbs the thermal expansion, plastic deformation, and the like of its constituent components.
Conventionally, for example, Japanese Published Patent No. 2785753 proposes securing good grounding between a chassis and the ground pattern of a circuit board by forming, in through holes provided in the ground pattern of the circuit board, a prepreg layer that protrudes through the through holes, and then metal-plating this protruding prepreg layer so that grounding between the chassis and the ground pattern of the circuit board will be achieved securely by way of the through holes.
Japanese Laid-Open Patent Application No. S63-158898 proposes a shielding structure for an RF circuit device in which good grounding is secured by forming, on the ribs of a chassis, projections made of soft metal, such as solder bumps, so that, when a circuit board is fixed to the chassis with screws, the projections will be deformed in such a way as to make close contact with the ground pattern of the circuit board.
Japan Institute of Invention and Innovation""s Journal of Technical Disclosure No. 94-10911 proposes forming, on the ribs of a chassis, projections that cut into a circuit board so that, when the circuit board is fixed to the chassis with screws, the projections will deform the circuit board in such a way as to secure good grounding.
These prior-art techniques all serve the purpose of securing good grounding, but simultaneously cause deformation in the circuit board and in the projections formed on the chassis ribs. This is undesirable in particular when, after initial assembly, the circuit board, chassis, or other component is found defective and thus reassembly is needed, or those components are used in a harsh temperature environment, because deformation, dents, and the like in the projections and in the circuit board remain and eventually degrade reliability and performance, as by making it difficult to secure stable grounding or by weakening the shielding effect.
On the other hand, Japanese Laid-Open Utility Model Application No. H4-43030 proposes placing a resilient grounding member between the grounding surface of a circuit board and the mount surface of a chassis so that, even if there are irregularities on the mount surface of the chassis, the grounding surface and the mount surface are kept in contact with each other uniformly.
This prior-art technique serves the purpose of securing good grounding, but not satisfactorily secure grounding with a converter for satellite broadcast reception, which is used in an extremely high frequency band.
An object of the present invention is to provide a structure for fixing a circuit board to a chassis that permits the grounding pressure with which the grounding pattern of the circuit board is kept in contact with the chassis to be distributed uniformly and that thereby permits secure grounding to be maintained even against violent variations in environmental conditions, vibrations, and other factors.
To achieve the above object, according to one aspect of the present invention, in a converter for satellite broadcast reception having a fixing structure that is provided with a circuit board, a plurality of radio-frequency circuits mounted on the circuit board and separated from one another by a grounding pattern, a chassis having ribs arranged in a pattern that corresponds to the grounding pattern, and a mount plate placed on the back surface of the circuit board, a rubber plate having resilience is placed between the circuit board and the mount plate.
According to another aspect of the present invention, in a converter for satellite broadcast reception having a fixing structure that is provided with a circuit board, a plurality of radio-frequency circuits mounted on the circuit board and separated from one another by a grounding pattern, a chassis having ribs arranged in a pattern that corresponds to the grounding pattern, and a mount plate placed on the back surface of the circuit board, the mount plate has rubber printed (formed) thereon in a pattern that corresponds to the grounding pattern.
These structures permit the grounding pressure with which the grounding pattern of the circuit board is kept in contact with the chassis to be distributed uniformly, and thereby permit secure grounding to be achieved in various environments.